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To evaluate the cardiovascular parameters spontaneous fluctuations and neural sympathetic discharge variability relationship during the gravitational stimulus, seven healthy males underwent ECG, blood pressure, respiratory and post-ganglionic sympathetic discharge activity (MSNA) recordings. Data were recorded at rest and during a 15-minute 80°head-up tilt followed by a step wise lower body negative pressure increase up to the onset of presyncope. Spectral and coherence analyses of systolic arterial pressure (SAP) and MSNA variability provided the indexes of vessels sympathetic modulation in the low frequency (LF) band, LF, and of the coupling between MSNA and SAP at LF, K(LF), during asymptomatic (T1) and presyncope (T2) periods of tilt. During T2, RR interval, SAP, LFmsna, LFand K(LF) values decreased compared to T1. in the presence of unchanged MSNA values. This result suggests that a significant coupling between SAP and MSNA variability in the 0.1 Hz band is mandatory for a proper orthostatic tolerance.

The study characterizes the sympathetic baroreflex control through the assessment of sympathetic baroreflex sensitivity (sBRS). sBRS was assessed as the slope of the regression line of the conditional probability of detecting a burst on the integrated muscle nerve sympathetic activity given an assigned diastolic arterial pressure (DAP) on DAP. sBRS was assessed during orthostatic challenge before and after 21 days -6 degrees head-down bed rest (HDBR) confinement. We identified an effect of the prolonged HDBR and an impairment of the sympathetic baroreflex just before pre-syncope symptoms induced by the orthostatic challenge, thus suggesting a possible role of the sympathetic baroreflex in the origin of neurally-mediated syncope.

Aging causes changes in cardiovascular control. The aim of the study was to analyze the effects of age on baroreflex sensitivity of healthy individuals of different ages, through cross-spectral analysis. One hundred and ten individuals divided into 5 age groups were evaluated. Heart period (HP) and systolic blood pressure (SBP) were derived from ECG and blood pressure signals recorded simultaneously for 15 minutes in the supine and orthostatic position. The gain of the transfer function from SBP to HP was taken as an index of baroreflex sensitivity (BRS gain ) and computed in low (LF) and high frequency (HF). In both positions and in both bands, BRS gain fell with age, thus suggesting a decrease magnitude of the HP response to SAP changes with age.

The present study exploited symbolic analysis of heart period (HP) variability during three different anesthetic strategies during neurosurgical procedures. We monitored HP variability in 93 patients during elective neurosurgical procedures. Patients were randomly assigned to three anesthetic strategies: sevoflurane+fentanyl (S-F), sevoflurane+remifentanil (S-R) and propofol+remifentanil (P-R). All anesthetic strategies were characterized by a reduction of HP variability. An increased presence of stable patterns was detected in the P-R group. Conversely, an increased presence of instable patterns was present in the second hour of surgery in S-F group. Despite an important reduction of HP variability, the symbolic analysis differentiates anesthetic strategies.

Complexity of R-R intervals (RR) and systolic arterial pressure (SAP) variability were computed to detect the aging process influence over cardiovascular control in resting supine (REST) and standing position (STAND). One hundred healthy subjects were divided into five groups (n=20 for each), according to age: 21-30; 31-40; 41-50; 51-60; 61-70. The RR and SAP series were recorded for 15 minutes at REST and STAND. Short sequences of RR and SAP were analyzed by conditional entropy. At REST, RR complexity showed reduction with age in 61-70, and SAP complexity decreased, starting from 31-40. Changes in cardiovascular control complexity, induced by STAND, reveal the difficulty of elderly individuals in dealing with sympathetic stressors.

The study compares permutation and coarse-grained entropy approaches for the assessment of short-term complexity of the cardiovascular control from heart period (HP) variability recordings. Approaches were applied to simulations and to HP variability series recorded during complete vagal blockade obtained via administration of a high dose of atropine (AT). Differences between the estimated complexity indexes derived from both simulations and real data indicated that permutation entropy has a larger sensitivity to noise than coarse-grained entropy. We recommend caution in applying permutation entropy in presence of short HP variability series characterized by a low signal-to-noise ratio such as after complete vagal blockade induced by AT.

Entropy-based approaches are frequently used to quantify complexity of short-term cardiovascular control from spontaneous beat-to-beat variability of heart period (HP) and systolic arterial pressure (SAP). Among these tools the ones optimizing a critical parameter such as the pattern length are receiving more and more attention. This study compares two entropy-based techniques for the quantification of complexity making use of completely different strategies to optimize the pattern length. Comparison was carried out over HP and SAP variability series recorded from 12 Parkinson's disease (PD) patients without orthostatic hypotension or symptoms of orthostatic intolerance and 12 age-matched healthy control (HC) subjects. Regardless of the method, complexity of cardiovascular control increased in PD group, thus suggesting the early impairment of cardiovascular function.

This study assesses complexity of cardiovascular control in patients affected by type-1 variant of long QT(LQT1) syndrome. Complexity was assessed by refined multiscale entropy of heart period (HP) and QT interval variabilities. HP was taken as the time distance between two consecutive R peaks (RR) and QT interval was approximated as the time distance between the R-peak and T-wave apex (RTa) and between R-peak and T-wave end (RTe). RR, RTa and RTe intervals were automatically extracted from 24h Holter recordings and the daytime period was analyzed (from 02:00 to 06:00 PM). Non mutation carrier (NMC) individuals (n=11), utilized as a control group, were taken from the same family line of the mutation carrier (MC) subjects (n=26). We found that, while NMC and MC groups were indistinguishable based on time domain and complexity analyses of RR dynamics, complexity analysis of RTa and RTe variabilities clearly separates the two populations and suggests an impairment in the cardiac control mechanisms acting on the ventricles.